This invention relates to pneumatic tires and more particularly to a novel carcass structure specifically for use in aircraft tires.
An aircraft tire is subjected to extreme operating conditions which include very high internal pressure, high speeds in excess of 300 kilometers per hour, and very high deflections. During taxiing and takeoff, the deflection may be more than 30%, and on landing 45% deflection or more under impact conditions. These extreme pressures, loads and deflections put the sidewall between the shoulder of the tire and the bead to severe tests. The high pressure and loads place the ply cords under severe tensile loads. The cords in the plies, particularly in the lower sidewall area, are frequently mechanically fatigued due to high heat buildup near the beads while the aircraft is taxiing or during takeoff.
In the prior art, it has been conventional to increase the number of plies of the tire to increase rigidity and to decrease deformation under load. Also much work has been directed to reinforcing the ply turnup portion of tires to improve durability.
U.S. Pat. No. 5,105,865 by Togashi et al. describes these conventional solutions and proposes that the durability of the tire can be improved by avoiding bending deformations of the ply surfaces. The patent describes a tire curvature that permits an increase in durability to be achieved with no increase in weight.
U.S. Pat. No. 4,029,137 by Robert Suydam teaches that an improvement in durability can be achieved by a novel wrapping of the ply structure about the beads. This invention also improves durability without increasing weight.
In British Patent GB 2 087 806 to Kaisha, a bias aircraft tire is disclosed wherein cords of the carcass plies are spaced further apart to achieve improved durability.
In addition to the normal loading conditions of aircraft tires military aircraft, in particular naval airships often are required to land on the decks of aircraft carriers. The landings are routinely harsh and rapid due to the shortened landing area. To stop the aircraft, an arrestor cable is employed. The nose wheel or main landing gear wheel of the aircraft impacts this 15/8 inch diameter arrestor cable on landings and can severely damage the tire. On the F/A-18E/F naval aircraft the main tire can see a camber angle of 10.2.degree.. This means that one sidewall will take the initial impact at about five times the normal rated load. This pinches the impacted sidewall severely which can result in cut or damaged carcass plies. Repeated landings result in cumulative damage. To extend the life of the main tire additional full width carcass plies have been used; however, this imposes a weight penalty.
The present invention discloses a novel approach to improve sidewall durability while enabling a reduction in overall tire weight.